1. Field of the Invention
This invention relates to a method and apparatus for obtaining samples of blood for diagnostic purposes.
2. Discussion of the Art
The prevalence of diabetes has been increasing markedly in the world. At this time, diagnosed diabetics represent about 3% of the population of the United States. It is believed that the total actual number of diabetics in the United States is over 16,000,000. Diabetes can lead to numerous complications, such as, for example, retinopathy, nephropathy, and neuropathy.
The most important factor for reducing diabetes-associated complication s is the maintenance of an appropriate level of glucose in the blood stream. The maintenance of the appropriate level of glucose in the blood stream may prevent and even reverse many of the effects of diabetes.
Glucose monitoring devices of the prior art have operated on the principle of taking blood from an individual by a variety of methods, such as by needle or lancet. An individual then coats a paper strip carrying chemistry with the blood, and finally inserts the blood-coated strip into a blood glucose meter for measurement of glucose concentration by determination of change in reflectance.
The medical apparatus of the prior art for monitoring the level of glucose in the blood stream required that an individual have separately available a needle or lancet for collecting blood from the individual, strips carrying blood chemistry for creating a chemical reaction with respect to the glucose in the blood stream and changing color, and a blood glucose meter for reading the change in color indicating the level of glucose in the blood stream. The level of blood glucose, when measured by a glucose meter, is read from a strip carrying the blood chemistry through the well-known process of reading reflectometers for glucose oxidation.
Generally lancets comprise a blade and a pressable end opposed thereto, with the blade having an acute end capable of being thrust into skin of a human. By striking the pressable portion, the acute end of the blade will pierce the skin, for example, of the finger. The finger lancet is primarily used to obtain small volumes of blood, i.e., less than 1 mL. Diabetics use the finger lancet to obtain volumes of blood less than 25 xcexcL for analysis for glucose. A small amount of blood for the blood test will ooze out of the skin. There are many small blood vessels in each finger so that a finger can be squeezed to cause a larger drop of blood to ooze. The finger is one of the most sensitive parts of the body; accordingly, the finger lancet leads to even more pain than what would be experienced by collecting blood via lancet at a different body site. The finger lancet presents another problem because of the limited area available on the fingers for lancing. Because it is recommended that diabetics monitor their blood glucose levels four to six times per day, the limited area on the fingers calls for repeated lancing of areas that are already sore. Because fingers are sensitive to pain, it is a recent tendency that the arm is subjected to blood sampling. See, for example, U.S. Pat. No. 4,653,513. The device of U.S. Pat. No. 4,653,513 comprises a cylindrical housing and a lancet support, which has a gasket or flexible portion slidably accommodated in the housing. Springs will retract the lancet support to thereby reduce air pressure in the housing so that it sucks a blood sample, automatically and immediately after a lancet pierces the skin. See also U.S. Pat. No. 5,320,607, which discloses a device comprising a sealed vacuum chamber in a state of preexisting reduced pressure, a support member for the sealed vacuum chamber, the support member defining a suction portion adjacent the sealed vacuum chamber, the suction portion, in cooperation with the sealed vacuum chamber, exposing an area of the skin of a patient to a reduced pressure state when the device is actuated, and means arranged within the suction portion for slightly rupturing a portion of the area of skin of the patient exposed to the reduced pressure state.
Because the blood volume requirements for a standard glucose test strip are typically 3 xcexcL or more, an area of the body that can generate that much blood from a lancet wound must be used. It is believed, however, that improvements in glucose test strip technology will reduce the volume of blood needed to 1 to 3 xcexcL. Because the finger is well supplied with blood and the amount of blood can be increased by squeezing the finger after lancing, the finger is the currently preferred body site for lancing, even though lancing of the finger is painful.
A less painful technique for obtaining body fluids is described in U.S. Ser. No. 08/982,721, filed Dec. 2, 1997. This application discloses an apparatus for obtaining blood for diagnostic tests. The apparatus comprises a housing having a sealable chamber located therein and a sealable opening in fluid communication with the sealable chamber, a power source, a vacuum pump operably connected to the power source, the vacuum pump in communication with the sealable chamber, a lancing assembly positioned within the sealable chamber, and a fluid collector positioned in the sealable chamber, the fluid collector in fluid communication with the sealable opening. It would be desirable to improve that apparatus in order to ensure that the fluid collector is properly positioned in the apparatus during the lancing and fluid collecting steps.
This invention provides a method and apparatus for collecting a sample of blood from a patient for subsequent diagnostic tests, e.g., glucose monitoring.
In one aspect of the invention, an apparatus for collecting a sample of body fluid, e. g., blood, for analysis in a diagnostic test is provided. In a preferred embodiment, the apparatus comprises:
(a) a housing having a sealable chamber located therein and a sealable opening in fluid communication with the sealable chamber;
(b) a vacuum pump in communication with the sealable chamber;
(c) a device for forming an unobstructed opening in an area of skin from which a sample is to be collected, preferably a lancing assembly, the device positioned within the sealable chamber;
(d) a movable support for supporting and positioning a port for a fluid collector in the sealable chamber, the movable support capable of moving the port within the sealable chamber between a first position and a second position; and
(e) a stop for aligning the fluid collector.
In more preferred embodiments, the apparatus further comprises a power source, and the vacuum pump is operably connected to the power source. The stop aligns the fluid collector so that the fluid collector is capable of being properly positioned in the apparatus during the lancing and fluid collecting steps.
The fluid collector is preferably a test strip that contains at least one chemical reagent for conducting a diagnostic test, e.g., a test for determining blood glucose level. Typically the test strip has an opening formed therein, which opening is capable of being aligned with the sealable opening of the housing. A preferred device for forming an unobstructed opening in the area of the skin from which the sample of blood is to be collected is a lancing assembly, which comprises a lancet for forming an opening in the skin. Alternatively, the unobstructed opening in the skin can be formed by a laser or by a fluid jet. In the case of a lancing assembly, when the lancing assembly is triggered, the lancet of the lancing assembly passes through the opening of the test strip and the sealable opening of the housing to form an opening in the skin of the patient. The sample of body fluid, e.g., blood, is obtained from the opening formed in the skin of the patient. The opening of the test strip should be properly aligned with the sealable opening of the housing before the lancing assembly is triggered, because misalignment of these openings may result in one or more of the following undesirable occurrences: (1) an unsuccessful assay; (2) a longer period of time required to collect an adequate amount of sample; (3) extensive contamination of the apparatus by the sample. The movable support (d) and the stop (e) are designed to operate in concert to ensure that the opening of the test strip and the sealable opening of the housing are properly aligned. By designing the movable support to move the fluid collector port from a first position to a second position, the opening in the test strip can be properly aligned with the sealable opening in the housing, thereby ensuring that the assay can be conducted successfully.
The vacuum pump requires a power source. The power source can be disposed within the housing. Alternatively, the power source can be external to the housing. The vacuum pump can serve the dual purposes of (1) stretching the skin and (2) enhancing the collection of the sample of blood from the unobstructed opening in the skin. Preferably, the vacuum pump can serve the triple purposes of (1) stretching the skin, (2) increasing the availability of blood to the area of the skin from which the sample is to be collected, and (3) enhancing the collection of the sample of blood from the unobstructed opening in the skin.
The housing comprises a body and a cover. The sealable chamber is located within the cover. The cover is separated from the body so that the test strip can be inserted into a test strip port located in the volume that is to be enclosed by the cover when the cover is closed against the body of the housing. After the test strip is inserted in the test port, the cover is closed against the body to form a chamber that will be sealed when the sealable opening of the housing is placed in contact with the skin of a patient. Preferably, the body of the housing contains electronics having programmed instructions to control the vacuum pump to maintain the desired level of vacuum for the method of this invention.
The apparatus preferably contains valves, such as, for example, solenoid valves, for triggering the lancet of the lancing assembly and releasing the vacuum at the conclusion of the blood collection procedure. The apparatus can optionally contain a heating element to increase the availability of blood to the area of the skin from which the sample is to be collected.
In another aspect of the invention, a method for collecting a sample of body fluid, e.g., blood, for analysis in a diagnostic test is provided. In general, the method comprises the steps of:
(a) inserting a fluid collector into the port;
(b) aligning the fluid collector latitudinally and longitudinally so that an opening in the fluid collector is aligned with the sealable opening of the housing of the apparatus;
(c) placing the sealable opening of the housing against the skin of the patient;
(d) forming an unobstructed opening in the area of the skin from which the sample of blood is to be collected;
(e) aligning the fluid collector longitudinally so that an opening in the fluid collector is aligned with the sealable opening of the housing of the apparatus; and
(f) collecting the sample of blood from the unobstructed opening in the skin onto the fluid collector, with the aid of vacuum and stretching of the skin.
In order to insert a fluid collector into the support, the cover is separated from the body of the housing; then the fluid collector, e.g., a test strip, is inserted into the port for the fluid collector; and then the cover is closed against the body of the housing. The movable support is actuated to cause the port to move from a first position to a second position in order to align an opening in the fluid collector with the sealable opening of the housing of the apparatus.
In a preferred embodiment of the method, step (d) is preceded by the step of increasing the availability of blood in the portion of the skin from which the sample is to be collected. In this preferred embodiment, the availability of blood in the portion of the skin from which the sample is to be collected can be increased by means of a vacuum, which is applied to the surface of the skin in the vicinity of the opening prior to forming the opening in the skin. The vacuum causes the portion of the skin in the vicinity of the blood collection site to become engorged with blood. The vacuum also causes the portion of the skin in the vicinity of the blood collection site to become stretched.
An opening in this stretched portion of skin can be formed with a cutting or puncturing device, e.g., a lancet, or other device capable of forming an opening in the skin, e.g., a laser or a fluid jet. If a cutting or puncturing device is used to form the opening, it must be retracted from the opening prior to the step of collecting the sample of blood from the opening. This retraction will allow the unrestricted flow of blood through the opening. After the opening is formed, the movable support is moved from the first position to the second position in order to align the opening in the fluid collector with the sealable opening of the housing of the apparatus. Then a vacuum can be used to aid in collecting the sample of blood from the opening in the skin.
The method and apparatus of this invention provide several advantages over the methods and apparatus of the prior art. First, a sufficient amount of blood can be collected from parts of the body, other than the finger, for conducting glucose monitoring tests. Second, by rendering other parts of the body suitable for collecting blood, the use of a painful finger lance can be avoided. Third, by increasing the availability of blood at the site where the blood is to be collected, the period of time required for collecting the sample can be reduced. Fourth, by improving the registration of the opening in the fluid collector (e.g., test strip) with the sealable opening in the housing, both the likelihood that the lancet will strike a solid portion of the fluid collector during the lancing step and the likelihood that an insufficient amount of sample will be collected will be reduced. Because of these advantages, the diabetic patient is more likely to monitor glucose levels in the blood at the intervals prescribed by his doctor.